AR-10, LR-308, and how many others are there?

I am reasonably certain my next project is gonna be a big AR. This is the beginning, I know there are several different variations of the "AR-10, but that's about all I know. Other than it will be in 7mm SAUM, it will have a heavy 28 or 30 inch barrel, and of course accuracy is the most important attribute. (Disclaimer) I am not now, nor do I plan to shoot "1000 yard bench rest competition." So all you bench rest types, go find another thread to unleash your negative rhetoric on. With that being said, any helpful advice will be greatly appreciated. What I have in mind is a rifle capable of taking any antlered critter in North America at extended ranges.

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The number of makers that do proprietary stuff with the "large frame" AR's is pretty extensive since there is no "mill spec standard" so to speak.

The AR10, LR308, SR25, LAR-8 are the ones that come to mind first.

Of all the models to choose from...these are the ones I would consider brand specific for parts. Just about everything else will mate up to one of these 4.

The Armalite rolls with the likes of Noveske compatibility but they have offered a 2nd model option for use with DMPS/SR25 Mags...the uppers are stil only going to run on Armalite/Noveske

The LR308 I would consider to be the most common platform. 95% of companies that make a billet lower, design it for the LR308 style uppers.

The SR25 is kind of a hybrid. It has the appearance of the Armalite, but the guts of the DPMS. (actually DPMS has KAC guts, but that's not the point)

And the LAR-8 is just all kinds of proprietary and I don't know what fits it.

For the caliber choice you've got...you're going to have a hard time finding someone build it for you, and I wish you luck. It's going to be expensive and I would highly doubt that the one man I know of with experience doing the build, will actually build one to those specs...but as I said...good luck with the project.

And just to clarify...what do you consider "extended ranges" and what do you feel the 7mmSAUM and 28+ barrel will do to help you achieve that kill shot?

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As far as extended range. If you remember, I built my .25 WSSM for a 500 yard rifle. I'm planning this one to go beyond that to about a 1000. Some of the places I hunt in Northwest Oklahoma are similar to what you hunt up there in the great white north. Wide open prairies with some big hills interspersed. 300 pound whitetails and some slightly bigger mule deer.

I was thinking the longer barrel would give me back some of the velocity I'll undoubtedly loose by having to seat the heavier bullets deeper, to fit in the mag. What do you think?

As far as the 7mm, just better BC's for bullet weight compared to the .30.

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Yes, Carl at Accuracy Systems is the man to talk to when looking for a SAUM in the AR10 platform, but you're going to have to twist his arm to get him to build a 24" upper. The last I heard, his recommendation was that "IF" he does a 7mm SAUM...that it would be more toward the 20" length. As I said, good lucking asking him about the 28"
This isn't as much of an issue as you'd think it would be.

You're going to have PLENTY of energy from a bullet that size, going that speed anyway. It's UNMATCHED in the AR10 platform.
Being able to consistently hit MOA targets on your first shot is where things get interesting anyway.

You're "probably" only going to be able to run something like the 168gr VLD bullets at mag length without having seating depth issues anyway. And that's a best case scenario. Something like the 162Amax would probably even be best suited due to the relationship of high bc to weight ratio.

For example, if you run the 162Amax at a conservative 3050fps from a 24" barrel, you're looking at 23 MOA of elevation (6.6 mil) at 1000 yds and you're still carrying OVER 1000 lbs of energy. (at my bp of roughly 28.45 on most days)

Trying to seat something like a 180 VLD is probably possible, but you're going to run into the ogive getting way down at the case mouth and that's usually too deep to get the accuracy you usually want from a VLD. It's to much of a jump to the lands.
You can do the math with any bullet you want to see how much seating depth you'll have to work with.

Typical mag length is 2.800"
7mmSAUM Case length is 2.035"
A 180 VLD is 1.525" total and .825" from the base to ogive leaving .7" from the ogive to the tip.

If you add .7 (ogive to tip) to the length of a case, you're looking at a COAL of 2.735" if you seat a 180 VLD to so the ogive is at the case mouth (not recommended)...which only leaves you .065" to play with seating depth before you're out of mag length.

So it's possible, but not likely for accuracy. 168 VLD's will be a little better, but I still feel the 162 Amax to be about the ideal bullet for that platform.

Also, using a powder like RL17...you're going to hit pressure signs, long before you actually run out of case capacity, so seating a heavy bullet deeper doesn't really correlate to loss of velocity in the semi-auto.
With other powders, that may not be true.

I purchased a 300 SAUM Armalite Upper a while back and I've been happy as a pig in shat ever since. I've had 3 different bullets (185, 190 and 210 VLDs all shooting around 1/2 MOA) and I've take two of those rounds out to beyond a mile so far.
Longest game KO is 930 yds and I would have no hesitation in going out to 1200 or so.
With the .30 cal 190s VLDs that I'm currently running...I'm carrying almost the same energy at 1000 yds, that you could potentially get with the 162 Amax at the same range. So you're correct in the 7mm ballistics...it will just depend on what bullet ultimately get to shoot the best.

I've been planning to get a 2nd upper in 7mmSAUM built for 2 years now and just haven't gotten around to it.

__________________"We do not rise to the occasion...we fall to the level of our training."